This invention relates to sizing screens for use in vibrating screen devices for sizing particulate materials. While the invention is described with particular reference to its preferred application in aggregate production, those skilled in the art will recognize the wider applicability of the inventive concepts disclosed hereinafter.
Aggregate production generally is conducted through the use of units known in the art as screen plants, which may be mobile or stationary. The screen plant is positioned in a first suitable location and may be repositioned, if desired, as conditions demand. The screen plant generally includes a suitable conveyor system which carries the material to a vibrating deck assembly, normally including at least a first sizing deck and a second sizing deck. The material is deposited on the first sizing deck by the conveyor and particular sized aggregate is dropped through the first deck to the second deck. The second deck also is a vibrating screen deck intended to size the material a second time, passing desired small size material through the deck, and depositing more coarse material on the output side of the vibrating screen assembly. The small material is the desired product and is collected by suitable means for later use.
Screen decks of various constructions for use in vibrating deck assemblies are well known in the art. However, various conditions inherent in aggregate operations, for example, moisture, fineness, clay content and size irregularity, have hampered production. In some cases, these problems or conditions cause production to be seasonal in nature. Clay content and moisture in particular can cause vibrating screen deck assembly malfunction, resulting in increased maintenance cost and decreases in product output.
One solution to these problems has been the design of a vibrating screen deck which uses a plurality of parallel wire strands extending along a frame structure to delimit the bed of the screen. The wire strand form of screen bed has improved production of vibrating screen plants. However, wire screen devices, while generally showing promise in various aggregate installations, have been plagued with operational problems in the field. For example, one commercially available wire screen design employs a plurality of individual lengths of wire or wire strands, each of which is fed through relatively complicated mechanisms. Since applicational use of the screen bed often results in wear on the wire strands, wire strand breakage or wire strand wear commonly requires field replacement of the wire strand. With devices known prior to my invention, wire strand replacement is a formidable task when conducted in the field. Proper wire strand tension after replacement also is difficult to achieve, unless relatively expensive devices in the form of torque wrenches are available.
Use of a "crown" for a screen deck to distribute the material over the entire area of the deck, thereby increasing the efficiency of the screen, is an old expedient. That is to say, screen beds often have a curved cross section along their width dimensions. In wire screen designs, this is accomplished by bending the frame members used to support the wire strands. It has been conventional in wire screen designs to notch or groove the frame members so that each wire strand has a predetermined individual location on each frame member, those locations being aligned longitudinally along the screen deck. In prior art devices, operation of the apparatus often results in the displacement of one or more of the wire strands from its predetermined groove position so that the wire strand moves towards or away from adjacent wire strands along the bed. When a sufficient number of wire strands are so mispositioned, the screens can become blocked, or the sizing variation present in the output of the screen becomes unsatisfactory.
My invention overcomes these prior art deficiencies by utilizing a screen bed employing close ended wire loops positioned from end to end along the screen bed frame. Because of wire loop use, at least two strands of wire can be tensioned simultaneously, and means for tensioning the wire loops are provided on a first end of the frame. When breakage of a particular wire loop occurs, replacement is accomplished easily with the screen of this invention because of the simplified method and structure for inserting the wire loop in the wire screen. The wire screen also is provided with a second crown along the longitudinal length of the bed. The second crown helps to maintain tension on the wire strands during operational use, so that the wire strands maintain proper spacing along the bed. Consequently, screen maintenance is reduced, the desired output of the screen deck is predictable within a predetermined size tolerance, and overall plant production is increased.
One of the objects of this invention is to provide an improved wire screen having a plurality of wire strands arranged in double crown configuration.
Another object of this invention is to provide a wire screen employing continuous wire loops, extended over the axial length of the screen deck, sides of the wire loops defining wire strands of the deck.
Another object of this invention is to provide means for tensioning the wire strands of a screen deck more simply, efficiently, and economically than heretofore available.
Another object of this invention is to provide means for simultaneously tensioning a plurality of wire strands of a screen deck.
Another object of this invention is to provide simplified means for attaching the wire strands of a screen deck to the screen deck frame.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.